The invention relates to a spectral photoelectric measurement transformer of the type with an array of photoelectric transformer elements and dielectric interference bandpass filters disposed on a common filter support connected upstream of them for sensitizing the transformer elements to different wavelength ranges of the measurement light.
Known measuring systems equipped with such measurement transformers are the DTP70 systems made by the X-rite company and the SpectroDens systems made by the Techkon company. The measurement transformers of these devices use a matrix arrangement of 4×4 individual photoelectric detectors. A co-operating bandpass filter is positioned in front of each photoelectric detector. The gaps between the filters are filled with black (opaque) compound as a means of providing optical isolation to reduce scattered light.
Spectral measurement transformers of the generic type are of interest in a number of applications. In the field of color measuring technology, for example, they are used as integrated sensors for printers, where they provide an automatic color control system for the printing process.
The general requirements placed on such measurement transformers are that they should be of a compact design and that they should lend themselves to production on a mass scale at a very low manufacturing cost.
Generally speaking, measuring systems equipped with such a measurement transformer must permit a high degree of absolute color measuring accuracy irrespective of the media involved. This measuring requirement corresponds to a spectral resolution of more than 10 different wavelength ranges (filter channels) in the visible measurement range between 420 nm and 680 nm. The filter channels must therefore have a bandpass function with a half-width of 20 to 25 nm and continuously evaluate the visible measurement range without interruptions.
Providing more than 10 measurement channels with appropriate physical bandpass filters drives up the cost of the measuring system.